1. Field of the Invention
The present invention relates to a method for generating 3-dimensional radiation images from which 3-dimensional pixel data indicating pixel values of respective 3-dimensional points of a subject are obtained and, more particularly, a method 3-dimensional radiation images for medical treatment, typically 3-dimensional radiation thoracic images.
2. Description of the Related Art
Usually radiation images such as X-ray images have been widely used in medical diagnoses. For example, in the case of X-ray images, an X-ray which has passed through a subject is irradiated onto a phosphor layer (phosphor screen) to convert the X-ray to a visible light, this visible light is irradiated onto a silver halide film to form thereon a latent image, an X-ray image is obtained by developing this film, and the X-ray image thus obtained is used in diagnoses of diseases (hereinafter referred to as the "S/F method".) In this case, there has been a problem that developed X-ray films thus obtained will require a larger space for storage as the number of developed films increases and moreover it is toilsome to select and take out desired X-ray films for comparison in observation of a time-elapsed change of the condition of disease of the same subject (for example, a patient.) Lately, therefore, a system has been used which enables to obtain a reproduced image with high image quality and high diagnostic performance after an X-ray image formed on a silver halide film as described above has been read photoelectrically by the so-called film digitizer to obtain image signals and various image factors such as sharpness, dynamic range and graininess which determine the quality of image and the diagnostic performance for diagnoses of diseases have been improved through image processing of these image signals.
FIG. 1 shows an example configuration of the film digitizer.
An X-ray film on which an X-ray image has been recorded and developed is transferred by transfer rollers 2 along a transfer passage 1. This X-ray film is repeatedly scanned by a laser beam 7 emitted from a laser scanning system 3 in a direction normal to FIG. 1 while being transferred, thereby this X-ray film is raster-scanned in two dimensions. This laser beam 7 is attenuated in accordance with a density of each pixel of the X-ray image recorded on the X-ray film, then transmits the X-ray film and is received by a light receiving element array 5 whereby image signals which bear the X-ray image are generated. When the X-ray image is recorded on a photographic paper, a reflected light of the laser beam 7 irradiated onto this photographic paper is received by the light receiving element 4 and converted into image signals.
On the other hand, a system using an energy accumulating phosphorescent material (accelerated phosphorescence fluorescent material; photo-stimulable phosphor) has begun to be used instead of the above-described system using silver halide films. A system using this accelerated phosphorescence fluorescent material is such that an X-ray image is cumulatively stored on an accelerated phosphorescence fluorescent panel or sheet, which is made up by forming the accelerated phosphorescence fluorescent material in the shape of sheet or panel, by irradiating an X-ray which has passed through a subject onto the accelerated phosphorescence fluorescent panel (or sheet) and this X-ray image is photoelectrically read to obtain image signals and obtains a reproduced image after image-processing these image signals. The basic mode of this system is disclosed on the U.S. Pat. No. 5,859,527. In this case, the accelerated phosphorescence fluorescent material hereof refers to a phosphor material which internally stores part of radiation energy of a radiant ray such as an X-ray, .alpha. ray, .beta. ray or .gamma. ray for a certain period of time or a long period of time when the radiant ray is irradiated onto the accelerated phosphorescence fluorescent material and discharges a stored energy as an accelerated phosphorescence fluorescent light. The type of radiant ray whose energy can be easily stored, the wavelength of a excitation light which is prone to emit an accelerated phosphorescence fluorescent light and the wavelength of the accelerated phosphorescence fluorescent light to be emitted differ with the type of the phosphor material.
FIG. 2 is shows an example configuration of the system using the accelerated phosphorescence fluorescent panel.
The system shown in FIG. 2 is an example of a photographing unit and a reader unit which are independently arranged.
In the photographing unit 10, an X-ray generated by an X-ray generating part 11 is irradiated to a subject 12 standing on a photographing stand 14 and the X-ray 13 which has passed through the subject 12 is irradiated to the accelerated phosphorescence fluorescent panel 15, thereby an X-ray image of the subject 12 is cumulatively stored on this accelerated phosphorescence fluorescent panel 15. Hereinafter, the accelerated phosphorescence fluorescent panel may be referred to as "imaging plate" or "IP" for simplicity.
After the photography has been carried out as described above, the accelerated phosphorescence fluorescent panel 15 is taken out from the photographing stand 14 and set in the panel inserting part 21 of the reader unit 20. In this case, the accelerated phosphorescence fluorescent panel 15 can be set in a magazine. If the accelerated phosphorescence fluorescent panel 15 which should be set in the panel inserting part 15 is set in the magazine or the cassette, the panel 15 is transferred along the transfer passage 22 after it has been taken out from the magazine or the cassette, the X-ray image cumulatively stored in this accelerated phosphorescence fluorescent panel 15 is read in the reading part 23, and image signals are generated therefrom. The configuration of this reading part 23 is described in the following. Image signals generated by this reading part 23 are entered into an image processing part 25 through a signal transmission path 24, whereby appropriate image processing such as frequency emphasis processing is given to image signals, and further entered into an image displaying part 27 through a signal transmission path 26, then the X-ray image of the subject 12 is displayed, for example, on the CRT display screen. In place of the image displaying part 27 for displaying the image obtained or together with this image displaying part 27, an image recording unit such as a laser printer, not shown, can be provided to reproduce and record an X-ray image, for example, on a silver halide film and obtain the X-ray image as a hard copy through developing treatment.
The accelerated phosphorescence fluorescent panel 15 which is read by the reading part 23 is transferred to an erasing part 29 along the transfer passage 28. This erasing part 29 irradiates an erasing beam onto this accelerated phosphorescence fluorescent panel 15 to erase the energy (visual persistence or after image) which remains on the accelerated phosphorescence fluorescent panel 15. The accelerated phosphorescence fluorescent panel 15 on which this after image is erased is transferred to the panel takeout part 31 along the transfer passage 30, taken out from the reader unit 20 and set on the photographing unit 10 for repeated use.
FIG. 3 shows a configuration example of the other system using the accelerated phosphorescence fluorescent panel. In FIG. 3, the components of the system corresponding to those of the system shown in FIG. 2 are given the same numbers and only the differences are described.
The system shown in FIG. 3 is provided with a stand-alone type photographing unit 40 in which the photographing stand 14 of the photographing unit 10 and the reader unit 20 are arranged integrally. Photography is carried out using the accelerated phosphorescence fluorescent panel 15 set in the photographing part 31 and the accelerated phosphorescence fluorescent panel 15 is transferred to the reading part 23 and read therein , then transferred to the erasing part 29 along the transfer passage 28 for erasing the after image, and further set again in the photographing part 31 along the transfer passage 30 for following photography.
FIG. 4 shows a configuration example of the reading part 23 shown as a block in FIGS. 2 and 3.
The accelerated phosphorescence fluorescent panel 15 on which the X-ray image is cumulatively stored is transferred (sub-scanned) by transfer rollers 100 in a direction indicated with arrow Y in the reading part shown in FIG. 3.
During this transfer (sub-scanning), a laser beam 102 emitted as an excitation beam from the laser beam source 101 is repeatedly reflection-deflected by a scanner 103 such as a galvanometer mirror or a polygon mirror, passes through a beam shape correcting optical system 104 such as a f.theta. lens and is irradiated onto the accelerated phosphorescence fluorescent panel 15 after having been reflected by the reflection mirror 105, thereby the accelerated phosphorescence fluorescent panel 15 is repeatedly scanned (main scanning) by the laser beam 102 in the direction of arrow X. An accelerated phosphorescence fluorescent light which bears an X-ray image cumulatively stored on the accelerated phosphorescence fluorescent panel 15 is emitted from respective scanning points. This accelerated phosphorescence fluorescent light is condensed by a condenser 106 such as an optical fiber array or the like, guided into a photo-multiplier tube 108, which cuts off the excitation light and transmits the accelerated phosphorescence fluorescent light passes, through an optical filter 107 and converted to electric signals. The accelerated phosphorescence fluorescent light can be directly received by providing, for example, a CCD optical sensor to which an optical filter which transmits only the accelerated phosphorescence fluorescent light at the front side without using the condenser 106.
Electric signals obtained through the photo-multiplier tube 108 are converted to digital image signals S by an A/D converter 110 after having been logarithmically amplified by a logarithmic amplifier 109. A sampling timing in this A/D converter 110 is controlled by the A/D conversion control part 113. These digital image signals S are directly stored in a storage medium 112 such as a magnetic disk or an optical disk after they have been stored temporarily in a frame memory 111 or without passing through the frame memory 111. Subsequently the image signals stored in this storage medium 112 are read out and entered into the image processing part 25 shown in FIGS. 2 and 3.
It is recognized that, in the system using this accelerated phosphorescence fluorescent material, an energy of the radiant ray to be irradiated onto this accelerated phosphorescence fluorescent material and a quantity of light of the accelerated phosphorescence fluorescent light to be emitted from irradiation of the excitation light are proportional to each other in a wide range of energy, a ratio can be changed in accordance with the quantity of excitation light. Therefore, a radiation image which will not be affected by a change of an exposure dose of the radiant ray can be obtained and photographic errors can be reduced. In a system for obtaining X-ray images of a human body, the exposure dose of the radiant ray to a human body can be reduced.
Both a system using the film reader and a system using the accelerated phosphorescence fluorescent material are able to obtain digital image signals and therefore these systems are featured in that less space is required for storage and information retrieval is easy and furthermore image processing can be carried out.
Problems to be Solved by the Invention
Along with an increase of cases suffering from lung cancer in recent years, it has been demanded to merely implement in a simple way not only generation and display of radiation images but also a method of determination of a malignant tumor and a benign tumor from radiation images or accurate detection of a 3-dimensional position of the tumor. When the presence of a disease is suspected on an image obtained from simple photography, a front view photography and a side view photography or, if required, a perspective view photography have usually been carried out and, in addition, dorsoventral and ventrodorsal photography have been carried out to detect a position of an affected portion. Thus, means has been carried out for estimating the position of the affected position of a case from slight positional deviations to be found on a plurality of images which necessarily form a magnified photography and this means has been sufficient only for detection of the affected position. However, those who are able to practise this means need be physicians having sufficient knowledge and moreover high level medical knowledge and experience are required to know what the position of the disease such as a tumor which has been obtained means. In other words, it is important to know what types of blood vessels, bronchi, etc. are present at that portion and therefore physicians build up a 3-dimensional structure in their heads and estimate the condition of the disease. In addition, the physicians estimate the nature of tumor as to whether it is located near a pulmonary trunk or a pulmonary vein and reconfirm the accurate position of the affected portion and diagnose more accurately a true nature of the tumor through tomography, CT scan or contrast photography.
These diagnostic techniques have been established and do not include remarkable disadvantages. For detecting the affected portion more precisely, however, it has been attempted to display a 3-dimensional blood vessel structure on the CRT by using a calculator graphic technology based on the information from angiography (DSA), tomography or CT scan. This technology enables to indicate a position of the blood vessel nearby which the tumor in question is located and therefore the estimation accuracy of the nature of tumor has been improved. However, this technology is disadvantageous in that the estimation of an affected portion based on interpolation from information which is not 3-dimensionally continuous is only the estimation, a great deal of calculations are required and, if a photographic interval is inappropriate, the difference will be large. Those equipment for tomography and CT are originally expensive.
In addition, the inventor and others found a considerable problem as described below as a result of studies on two-dimensional radiation images, which can be 3-dimensionally viewed as a stereoscopic vision, by photographing the same subject in directions which deviate from one another as far as an angle corresponding to a parallax with respect to thoracic radiation images. Specifically, since the chest behaves as the heart beats, the relation of 3-dimensional positions is disordered during two or more times of photography for which a position of an X-ray bulb for stereoscopic vision has been changed This is the same with the X-ray CT and the MRT which are required for many hours in photography or measurement and an artifact due to respiration and physical motion is unavoidable. In simple X-ray photography or contrast photography, the position deviation can be substantially reduced by replacing the radiation sensor within an extremely short period of time. In photography for obtaining, for example, two images within 0.1 second, the above problem as to the positional deviation can be largely solved by photographing the images within one or two seconds in synchronization with respiration, electrocardiography or pulse waves. On the other hand, in such photography, 3-dimensional positions could not be completely aligned due to the presence of physical motion. Though this is remarkably observed particularly in obtaining stereoscopic thoracic radiation images, the pulsation of blood is unavoidable as well as in the chest with a further problem of physical motion in photography of radiation images of animals including human bodies and therefore the above problem is common to the radiation images of all parts of a body. This is clearly the same with the subjects, which behave quickly in a short period of time, other than human bodies.